As is known in the art, mask layers, preferably hard mask layers, are deposited on semiconductor devices in order to structure the semiconductor devices in a predetermined manner. For photolithographically structuring the semiconductor device and/or the mask layer, a photo resist is commonly used. Such a photo resist is generally patterned by exposing the resist to electromagnetic waves of a predetermined wave-length range and patterned with a pattern device.
A cross-sectional view of a portion of a semiconductor device is shown in FIG. 2 which illustrates a semiconductor device 10, constituted preferably of Si, wherein as an example, a recess 11 has basically a rectangular shape in the cross-section of FIG. 2. A mask 12, preferably a carbon hard mask with a thickness of 170 nm as an example, is deposited on the semiconductor substrate 10. On top, a liner 13, preferably SiON with a thickness of 60 nm as an example is deposited according to FIG. 2.
For the structure shown in FIG. 2, a known stripping process for removing a photo resist (not shown in FIG. 2) mask was utilized. The resist was a carbon-type film which was removed by an oxygen-based etchant. The etchant plasma comprised for example 2000 sccm O2 as well as 100 sccm N2 at a pressure of e.g. 150 Pa and a temperature of 250° C. While stripping the photo resist on top of the liner layer 13, e.g. SiON, cavities 14 were formed in the carbon hard mask 12 as a parasitic side effect. Such erosion cavities 14 in the carbon hard mask 12 are highly undesirable since it leads to the etching of undesired features during subsequent processing. The formation of the cavities 14 is based on the attack of the carbon hard mask 12 by the oxygen rich plasma process used during the resist rework step at areas of weakness, especially at edges, corners and strongly bent portions of liner layer 13
FIG. 3 shows a structure basically similar to the structure according to FIG. 2 except that the cavities 14 and therefore the erosion of the carbon hard mask 12 on the semiconductor substrate 10 is substantially more pronounced. Leading to the structure of FIG. 3, a wet etch process was carried out three times to remove a photo resist (not shown in FIG. 3) from the surface of liner 13. Here, the vast cavities 14 formed in the carbon hard mask 12 on top of the semiconductor substrate 10 also result from the attack of the carbon hard mask by the wet etchant used during the resist stripping process at areas of weakness in the SiON liner layer 13.